Iron blue pigment



Patented Mar. 10, 1942 IRON BLUE PIGMENT Paul A. Thomasset, St. George, Staten Island,

N. Y., assignor toAnsbacher Siegle Corporation, New York, N. Y., a corporation of New York ' No Drawing. Application November 15,1939,

Serial No. 304,547

1 Claim.

The present invention relates to the manufacture of colors of the general type knownas "iron blues including Prussian blue. More particularly, it concerns the manufacture of iron blues of a type having a high resistance to alkalies. These colors have a range of shadesvarying in accordance with steps practised in the process of production that are well known in the art and have a wide range of application in the printing ink, paint, lacquer and pigment fields generally. However, iron blue pigments are very deleteriously aiiected by alkalies and as these colors are very frequently applied to uses where they come into contact with alkalies, they are frequently spoiled. For instance, when a soap wrapper is printed with Prussian blue, if sufiicient moisture is present to dissolve the soap, the wrapper will be seriously marred and made unpresentable by reason of the fact that the ink will be changed from a rich deep blue color to a muddy yellow, and thewhole appearance of the wrapper thus spoiled.

These colors aregenerally considered to be a precipitate of ferric ferrocyanide and formerly were made by precipitating potassium ferrocyanide by ferrous sulphate and then by oxidizing the bluish white precipitate thus formed to a darker blue, the commercial Prussian blue.

More .recently, iron blues have been produced by precipitating sodium ferrocyanide with ferrous sulphate in the presence of ammonium sulphate and acid, usually sulphuric-acid. The resulting precipitate is then oxidized by means of various oxidizing agents, such as sodium chlorate and sodium bichromate at a temperature of about amount of sodium sulphate 75 C., and the product is then filtered, washed freeof soluble salts, and dried in the usual manner; The pigment so obtained is very satisfactory and in every respect the equal of if not superior to the potassium ferrocyanide product. It has, however, like all ironhlues heretofore produced, a very great susceptibility to the action of alkalies, and the color is very deleteriously afiected if it comes into contact therewith.

It is a principal object of the present invention to provide an iron blue .that will have a very high resistance to the action of alkalies, even such strong alkalies as caustic soda.

It may be said broadly that this result is obtained, according to the present invention, by taking such steps in the process oi-the manufacture of the iron blues as to reduce the oil absorption very considerably and by adding salts of certain metals of the iron group which have the ef-' feet of greatly increasing the resistance of the I color to the action of alkalies.

The first result, namely, that of reducing the oil absorption of the pigment, is in the preferred process attained by adding an excess of sodium sulphate prior tothe precipitation of the whitish precipitate. It is to be noted here that in the normal reaction of the ingredients that throw down this whitish precipitate, sodium sulphate is always formed because of the reaction of the sodium ferrocyanide with ferrous sulphate which yields ferrous ferrocyanide and sodium sulphate. However, it is contemplated, according to the process of this invention, to add free sodium sulphate to a solution of ferrous sulphate, ammonium sulphate, and sulphuric acid, all. these ingradients being dissolved in water at a temperature of about 30 C. This addition of sodium sulphate is a departure from the usual formula of manufacture which normally resuits'in the undesiredand unavoidable production of a large due to the above described reaction which takes place upon the addition of sodium ferrocyanlde in an aqueous solution at 30 C.

Upon the addition of the sodium ferrocyanide, precipitation takes place. The precipitate is raised to a temperature of 75 C. and salts of certain metals of the iron group, such as nickel sulphate. .or cobalt chloride, are added. The product resulting has a very high degree of resistance to the action of alkalies.

A formula according to the present invention follows:

First, a solution in water at about 30 C. is made of /2 k. of ferrous sulphate, 21.4 k. of ammonium sulphate, 15 k. of sodium sulphate, and 2.1 k. of 66 Baum sulphuric acid in 500 liters of water. To this is added a solution of 100 k. of sodium ferrocyanide dissolved in 1,000 liters of water at 30 C. which is added slowly with stirring. Upon precipitation, the temperature is increased to C. and 3.5 k. of nickel sulphate dissolved in 50' liters -of water is added. The whole is stirred for a few minutes and an additional portion of 24.4 k. of sulphuric acid 66' and strength and oil absorption of the pigment can be obtained by variations in temperature and in the concentrations of the ingredients.

Instead of nickel sulphate or cobalt chloride, other nickel salts or cobalt salts may be used, such as nickel ammonium sulphate and nickel chloride, and other water soluble nickel and cobalt salts which also give substantially the same high resistance to alkalies. In fact, the addition of both nickel sulphate and cobalt chloride added upon precipitation gives very excellent results.

Sodium sulphate is, of course, a soluble saltand, regardless of whether it is produced by the reaction of the ferrous sulphate and sodium ferrocyanide or whether it is added in the free state, it? is eliminated during the washing and drying step and does not appear in the ultimate product.

The process of this, invention is, of course, not

limited to iron blues produced by the sodium ferrocyanide process described above as a preferred process, but is applicable to the potassium ferrocyanide process referred to hereinabove and .thus forming a white precipitate; raising the temperature of the precipitate to about 75 C. and adding a solution of nickel sulphate to said precipitate and oxidizing the mass to a blue color by the addition of sulphuric acid and an aqueous solution of sodium chlorate.

PAULA. THOMASSET. 

